1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly, to a solid state image pickup device and a method of fabricating the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for a solid state image pickup device and a method of fabricating the same for improving sensitivity of the semiconductor device.
2. Discussion of the Related Art
A conventional solid state image pickup device includes a plurality of photoelectric conversion regions having photodiodes (PD), a vertical charge coupled device (VCCD) region between the plurality of photoelectric conversion regions and transferring the charge generated in the photoelectric conversion regions in a vertical direction, a horizontal charge coupled device (HCCD) region transferring in a horizontal direction the charge transferred from the VCCD region in the vertical direction, and a floating diffusion region sensing and amplifying the charge transferred in the horizontal direction and outputting it to a periphery circuit.
A conventional solid state image pickup device and a manufacturing method thereof will be explained with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view showing the structure of a conventional solid state image pickup device and FIGS. 2A to 2C are cross-sectional views showing the process steps of fabricating the conventional solid state image pickup device.
As shown in FIG. 1, a conventional solid state image pickup device includes a plurality of photoelectric conversion regions 8 converting ah image signal of incident light into an electrical signal and formed in a p-well region 2 of an n-type substrate 1, charge coupled device (CCD) channel regions 4 formed between the photoelectric conversion regions and transferring the image charge generated in the photoelectric conversion regions 8 in a vertical direction, a channel stop layer 3 around each of the plurality of photoelectric conversion regions 8, a plurality of first and second polygates 6 and 7 insulated from each other by an insulating layer 5 over the CDD channel regions 4 and overlapping with each other in a predetermined area, a metal shading layer 9 formed on the insulating layer 7 exclusive of a portion over the photoelectric conversion region 8, an interlayer insulating layer 10 formed on the entire surface including the metal shading layer 9, a planarizing insulating layer 11 formed on the interlayer insulating layer 10, a color filter layer 12 formed on the planarizing insulating layer 11 over the photoelectric conversion layer 9, a top coating layer 13 on the entire surface including the color filter layer 12, and a microlens 14 formed on the top coating layer 13 focusing light image signal onto the photoelectric conversion region 8.
A method of fabricating a solid state image pickup device will be explained with reference to the accompanying drawings.
Referring to FIG. 2A, a p-well 2 is formed on an n-type substrate 1. Next, pixels and a channel stop layer 3 isolating the pixels from one another are formed in the p-well 2. Subsequently, an ion implantation process for a buried charge coupled device (BCCD) is carried out to form CCD channel regions of VCCD and HCCD regions.
Referring to FIG. 2B, a gate insulating layer is formed on a polysilicon layer deposited on the entire surface including the CCD channel regions 4. Subsequently, the polysilicon layer is patterned to be left over predetermined portions of the CCD channel regions 4 to form first polygates 5. Then, another insulating layer for insulating electrodes from one another is formed on the entire surface including the first polygates 5. Thereafter, a polysilicon layer is deposited and then patterned to be left over the first polygates 5 to form second polygates 6.
Subsequently, an insulating layer is formed on the entire surface including the second polygates 6. Next, an n-type ion implantation process is carried out to form a photodiode region and then a p-type ion implantation process is carried out to complete a photoelectric conversion region 8. A metal shading layer 9 is formed on the insulating layer exclusive of a portion over the photoelectric conversion region 8, so that the light is transmitted only to the photoelectric conversion region 8. Thereafter, an interlayer insulating layer 10 is formed on the entire surface including the metal shading layer 9 to protect the surface of the metal shading layer 9.
Referring to FIG. 2C, a planarizing insulating layer 11 is formed on the interlayer insulating layer 10. A color filter layer 12 filtering specific wavelengths from the light is formed on the planarizing insulating layer 11 over the photoelectric conversion region 9. Next, a top coating layer 13 is formed on the planarizing insulating layer 11 including the color filter layer 12 and then a microlens 14 is formed on the top coating layer 13. Then, a pad-opening process is carried out for a wirebonding process (not shown).
In the a conventional solid state image pickup device, the light transmitted through a camera lens is focused by the microlens 14 and only specific wavelengths from the light is irradiated to the photoelectric conversion region 8. The irradiated light to the photoelectric conversion region 8 is converted into the image charge to be transferred through the CCD channel regions 4 to a floating diffusion region (not shown). The transferred image charge is sensed and amplified in the floating diffusion region and then is transferred to a peripheral circuit.
However, a conventional solid state image pickup device and a method of fabricating the same have the following problems.
First, a light-receiving area is not wide enough in a photoelectric conversion region because the CCD channel regions and the photoelectric conversion region have a same planar structure. The amount of received light thus is not enough to obtain a good image sensitivity.
Second, since the photoelectric conversion region is located far from the microlens, the amount of light transmitted into the photoelectric conversion region is limited when the light is irradiated in a tilted direction. Moreover, since the light is not completely refracted against the microlens, the nonirradiated light into the photoelectric conversion region is scattered. Thus, to the conventional solid state image pickup device has a poor image sensitivity due to a smearing effect in the photoelectric conversion region.